The use of high-performance composite fiber materials is becoming increasingly common in applications such as aerospace and aircraft structural components. As is known to those familiar with the art, fiber reinforced composites consist of a reinforcing fiber such as carbon or KEVLAR and a surrounding matrix of epoxy, PEEK or the like. Most of the composite materials are formed by laminating several layers of textile fabric, by filament winding or by cross-laying of tapes of continuous filament fibers. However, all of the structures tend to suffer from a tendency toward delamination. Thus, efforts have been made to develop three-dimensional braided, woven and knitted preforms as a solution to the delamination problems inherent in laminated composite structures.
For example, U.S. Pat. No. 3,834,424 to Fukuta et al. discloses a three-dimensional woven fabric as well as method and apparatus for manufacture thereof. The Fukuta et al. fabric is constructed by inserting a number of double filling yarns between the layers of warp yarns and then inserting vertical yarns between the rows of warp yarns perpendicularly to the filling and warp yarn directions. The resulting construction is packed together using a reed and is similar to traditional weaving with the distinction being that "filling" yarns are added in both the filling and vertical directions. Fukuta et al. essentially discloses a three-dimensional orthogonal woven fabric wherein all three yarn systems are mutually perpendicular, but it does not disclose or describe any three-dimensional woven fabric having a configuration other than a rectangular cross-sectional shape. This is a severe limitation of Fukuta et al. since the ability to form a three-dimensional orthogonal weave with differently shaped cross sections (such as T .parallel. T .parallel.) is very important to the formation of preforms for fibrous composite materials. U.S. Pat. No. 5,085,252 to Mohamed et al. overcomes this shortcoming of Fukuta et al. by providing a three-dimensional weaving method which provides for differential weft insertion from both sides of the fabric formation zone so as to allow for superior capability of producing three-dimensional fabric constructions of substantially any desired cross-sectional configuration.
Also of interest, Fukuta et al. U.S. Pat. No. 4,615,256 discloses a method of forming three-dimensionally latticed flexible structures by rotating carriers around one component yarn with the remaining two component yarns held on bobbins supported in the arms of the carriers and successively transferring the bobbins or yarn ends to the arms of subsequent carriers. In this fashion, the two component yarns transferred by the carrier arms are suitably displaced and zig-zagged relative to the remaining component yarn so as to facilitate the selection of weaving patterns to form the fabric in the shape of cubes, hollow angular columns, and cylinders.
Also, U.S. Pat. No. 4,001,478 to King discloses yet another method to form a three-dimensional structure wherein the structure has a rectangular cross-sectional configuration as well as a method of producing cylindrical three-dimensional shapes.
A four directional structure was developed by M. A. Maistre and disclosed in Paper No. 76-607 at the 1976 AAIA/SAE Twelfth Propulsion Conference in Palo Alto, Calif. The structure was produced from pultruded rods arranged diagonally to the three principal directions. This was compared to three-dimensional woven structures and it was found that the four directional preform was more isotropic than three-dimensional fabric structures and its porosity was characterized by a widely open and interconnected network which could be easily penetrated by the matrix whereas the porosity of three-dimensional structures was formed by cubic voids practically isolated from each other and having difficult access.
Other forms of four directional structures are disclosed in U.S. Pat. No. 4,252,588 to Kratsch et al. and U.S. Pat. No. 4,400,421 to Stover. One structure is oriented in the diagonal/orthogonal directions wherein two sets of yarns are oriented in the diagonal direction and the other two sets (axial and filling) are orthogonal to each other. The second structure has one set of yarn in diagonal direction and the other set of yarn being mutually orthogonal to each other.
Fukuta et al. constructed a three-dimensional multi-axial weaving apparatus as disclosed in U.S. Pat. No. 5,076,330. The apparatus has four elements consisting of a warp rod holding disk, weft rod insertion assembly (with weft rod feeding and weft rod cutter units), a reed and a take-up assembly. The apparatus produced a structure which has four sets of yarns comprising one set of warp (axial) and three sets of weft yarns oriented diagonally around the warp yarns.
Anahara et al. discloses a five yarn system multi-axial fabric in U.S. Pat. No. 5,137,058. The preform according to this invention has five sets of yarn used as warp, filling, Z-yarn and .+-. bias yarns that are oriented inside the preform. A machine for manufacturing the preform is disclosed comprising a warp, .+-. bias and Z-yarn beams to feed the yarns into the weaving zone, a shedding device which opens the warp layers for insertion of the filling yarns, screw shafts to orient the bias yarns, and rapiers for insertion of weft and Z-yarns into the preform structure. However, as known to those skilled in the art, the screw shafts do not effectively control the bias yarn placement and this causes misplacement of these yarns and eventually makes the Z-yarn insertion very difficult.